Posted by admin on 24th March 2010

Output Devices

Output devices allow you to sense what a computer is doing. Usually that’s through sight, but speakers allow use to hear as well. In this section, you’ll find there are at least a couple of devices that do the same thing, but choosing which one is most appropriate and knowing why is what the exam is looking for.

Output on Screens

There are two types of screen you need to know about: LCD (also called TFT) screens and CRT screens. The three letter names stand for the technologies that make them work, though you don’t need to memorize them. See what you can find about each technology – it will help you understand the differences.

CRT is an old technology – the very first screens on computers were CRTs. Obviously they’ve evolved since then – to be the very best screens in terms of colour matching real life and print. However, because of the big glass vacuum tube that makes them work, they are bulky, heavy and use a lot of energy to run.

LCD or TFT is the type of screen that are found on all laptops and almost all new computers. They’re “flat screens”, much thinner and lighter to put on your desk and use less energy. As the technology matures, they cost not much different to CRTs, which used to be much cheaper. The ability to display realistic colours is much better than 10 years ago, too – these are now the standard in screens. They don’t flicker like old CRTs had a bad reputation for, which makes them much nicer to use for long periods.

In portable devices, CRT was never an option – much too big, heavy and power-hungry. LCD is  the standard on laptops and mobile phones, although new technologies like AMOLED will start to take market share over the next few years.

Output on Paper

There are a few different options for outputting on paper, two of which you’ll likely see in normal life, some you won’t!

Dot Matrix Printers were some of the very first available for PCs. They work by physically hitting an inky ribbon onto paper with a grid op metal pins. That’s really noisy, slow, only black ink and has a poor resolution. They’ve been pretty much obsolete for more than 10 years – it would be a bit crazy for you to need to know any more than these basics.

Inkjet Printers work exactly like they sound – little “jets” of ink are splashed onto paper. Imagine painting with a Super Soaker, except really tiny and super accurate – only one minuscule drop hits the paper. This gives a much higher resolution and colour, so a much better image than any other technology available to normal consumers. Inkjet printers tend to be quite cheap to buy, but the ink can end up being really expensive, even more than a new printer. If you only print a few pages in a week, an inkjet might work out cheapest for you. If you need high-quality photos printed, an inkjet might be best for you too.

Comparing the cost of Inkjet and Laser Printers (click for a bigger view)

Laser printers (have no Z, it’s an S!) use a laser to make toner stick to the page. Toner is not wet like ink, but a dry powder, a black or coloured dust. It comes in big cartridges that cost the same as a little inkjet cartridge but print lots more pages. Even though a laser printer costs more than an inkjet to start with (after all it has a laser in it!), if you print a lot, like a school or an office, it will quickly turn out cheaper. Look at the graph to make sense of this!

Dye-sub and other types of printers are used by professional printing companies to get the types of image that are beyond laser and inkjet. These are usually produced on big, expensive machines that only a specialist company would buy.

Plotters are a specialist tool for creating images made up of lines, especially blue-prints and signs. The computer moves a pen or several pens across the paper, picking them up and pushing down on the paper to create the lines of the image. Clearly, this would not be helpful for printing out a photo, but drawing the components of a ship or a building for its designers is easy. They can be huge, creating massive documents for the builders use.

Other outputs

Most computers either have speakers built in or have some plugged in. The output of sound is great for watching videos, but think about the information you can get from the sound in a game – look left or right to see what’s making that noise!

Lights can be used by computers to tell us what’s going on – from a flashing LED telling you about the hard-disk to the network connection.

Many different robotic parts can be controlled by computers.  These too are outputs, whether smashing up other robots or building cars in a factory. The motors and components that make them work are carefully controlled and synchronised to do the precise moves needed. If this interests you, search for ASIMO or other robots to find out how they work.

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